Generally, an upper structure of a bridge is expanded or contracted due to temperature change, drying shrinkage, creep, etc., and is moved due to a dynamic load applied due to vehicle passage, an earthquake, etc. Therefore, an appropriate gap is provided between two neighboring upper structures according to the material, length, support structure, etc. of a bridge floor slab during the construction of the bridge. An expansion joint device is installed between upper structures, and a finger-type expansion joint device is frequently used.
Among expansion joint devices, when a modular joint is used in a place where the amount of expansion and contraction of upper structures is very large, the number of parts increases and the structure of the modular joint becomes complicated, making it difficult to achieve structural stability and economic efficiency.
When a finger joint system is used in a place where the amount of expansion and contraction of upper structures is very large, it is necessary to set a very large interval between two abutment points. Thus, the thickness of necessary fingers becomes too thick and exceeds the thickness of an ordinarily available iron plate. As a result, it is difficult to obtain the fingers on the market. In addition, when the thickness of the iron plate is too large, it is difficult to handle the iron plate because the steel plate is heavy, and it is very difficult to cut the steel plate into a finger shape and to smooth the surface of the finger.